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#### A.1.7 Accessing Global Variables in Oct-Files

Global variables allow variables in the global scope to be accessed. Global variables can be accessed within oct-files by using the support functions `global_varval` and `global_assign` from the current interpreter’s symbol table. Both functions take as first argument a string representing the variable name to be obtained or assigned. The second argument of `global_assign` is the value to be assigned. An example of the use of these two functions is

    #include <octave/oct.h>
    #include <octave/interpreter.h>

    DEFMETHOD_DLD (globaldemo, interp, args, , "Global Demo")
    {
      if (args.length () != 1)
        print_usage ();

      octave_value retval;

      std::string s = args(0).string_value ();

      octave::symbol_table& symtab = interp.get_symbol_table ();

      octave_value tmp = symtab.global_varval (s);

      if (tmp.is_defined ())
        retval = tmp;
      else
        retval = "Global variable not found";

      symtab.global_assign ("a", 42.0);

      return retval;
    }

An example of its use is

    global a b
    b = 10;
    globaldemo ("b")
    ⇒ 10
    globaldemo ("c")
    ⇒ "Global variable not found"
    num2str (a)
    ⇒ 42